Changes in the cytoskeleton of the pancreatic islets grown in monolayer cultures from dbdb, obob diabetic mice and normal littermates will be studied by immunofluorescent techniques during the transition from normal to diabetes. Cytoplasmic microtubules and microfilaments will be followed in vitro using antibodies to tubulin and actin. The investigation will be extended to the pancreatic islets in vivo through the use of transmission electron microscopy coupled with immunochemical techniques to localize microtubules and microfilaments. The cellular pools of polymerized and unpolymerized tubulin will be measured by colchicine binding and radioimmunoassay during the transition into the diabetic state. The biochemical factors which control the assembly and disassembly of the microtubules and microfilaments in alpha, beta and delta cells will be studied in detail. It is known that Ca ions is required for the secretion of the pancreatic hormones. This proposal will also analyze the presumed common denominator for mediating Ca ions stimulated secretory processes in pancreatic cells, the Ca2 ion-dependent regulator (CDR). The intracellular localization of CDR and the regulation of microtubules and microfilaments by CDR will be investigated in normal and diabetic animals. The relationship between insulin and somatostatin secretion will be probed by analyzing the effect of somatostatin on the cytoskeleton with changes in secretion of the two hormones in monolayer cultures. Thus, this proposal will define possible changes which may occur in the cytoskeleton. In addition, these investigations should elucidate the overall involvement of the microtubule - microfilamentous system in hormone secretion and regulation.